J.K. Simmons — INSANELY JACKED … For New ‘Justice League’ Flick

Well, now we know what the J in J.K. Simmons stands for — JACKED.  Check out the 61-year-old beasting out in an L.A. gym — gearing up for his role in the upcoming “Justice League” movie.  No, he’s not playing Bane … or Batman … he’s…